Tumors of the thoracic and lumbar spine commonly extend into the vertebral canal and impinge on the dura, often infiltrating its superficial layers. This infiltration of sarcoma cells into the dura surface is a major cause of failure of aggressive surgery to obtain cure of these patients. With external beam radiation therapy, the majority of the tumor bed can be treated to effective dose levels. However, because of the close proximity of the cord, the dose to the dura must be limited to well below the desired treatment range. Therefore, to increase the dose to the dural surface without over-irradiating the cord, it is proposed to intraoperatively deliver a supplemental dose using a specially made beta-emitting radioactive device. The additional dose delivered will, at very small risk and potentially great advantage to the patient, markedly increase the probability of tumor control. During Phase I of this program, a "proof of principle" device was developed. On the basis of the successful results of the Phase I program, physicians at the Massachusetts General Hospital have clinically employed the "proof of principle" device to successfully treat seven appropriate patients with vertebral or paravertebral tumors, and assess patient tolerance and outcome under an IRB approved protocol. Radiation oncologists who have employed the existing plaque design have identified a number of features that would result in improved dose delivery. The specific aim of this program is to further develop this brachytherapy device beyond the "proof of principle" developed during the Phase I program. A customizable geometry plaque will be developed to improve the conformity of the dose distribution to the treatment target. This will include differential loading to improve dose drop-off, an improved method of incorporating anatomical features into the plaque configuration, and methods for manufacturing completed plaques before activation to facilitate achieving more complex geometries and reducing the radiation hazard. The resultant plaque and its dosimetry will be evaluated for clinical utility through a human trial. The results of this evaluation will lead to an optimum design of this device, in preparation for clinical use.